This invention pertains to a process for the preparation of 2-aryl-2H-benzotriazoles and derivatives thereof. More particularly, the invention relates to a novel process for preparing 2-aryl-2H-benzotriazoles whereby high yields of the desired products are obtained and effluent pollution problems occurring with present processes for making such products are essentially eliminated.
Heretofore, the conversion of an ortho-nitroazobenzene to the corresponding 2-aryl-2H-benzotriazole has been accomplished by chemical and electrolytic reduction processes. For example, as seen in U.S. Pat. Nos. 3,072,585 and 3,230,194, o-nitroazobenzene derivatives have been chemically reduced utilizing zinc in alcoholic sodium hydroxide solutions to give good yields of the corresponding 2-aryl-2H-benzotriazoles. Ammonium sulfide, alkali sulfides, zinc with ammonia at 80.degree.-100.degree. C., sodium hydrosulfide and zinc with hydrochloric acid have also been used as the chemical reducing agents for this transformation as disclosed in U.S. Pat. No. 2,362,988. The use of ammonium sulfide was also reported by S. N. Chakrabarty et al, J. Indian Chem. Soc., 5, 555 (1928); Chem. Abst., 23, 836, (1929) with mixed results depending on the presence or absence of substituent groups on the 2-aryl group. In some cases the desired 2-aryl-2H-benzotriazoles were not formed at all with the products of reduction being only the corresponding o-aminoazobenzenes.
Electrolytic reduction of o-nitroazobenzenes was reported by H. Itomi, Mem. Coll. Sci. Kyoto Imp. Univ., 12A, No. 6, 343 (1929); Chem. Abst., 24, 2060 (1930) with the use of a copper cathode in dilute sodium hydroxide solution. Yields varied from 25 to 60% depending on specific embodiments and conditions with a major impurity being formed, namely the corresponding o-aminoazobenzene.
The widely used zinc dust and sodium hydroxide chemical reducing system for transforming o-nitroazobenzenes into the corresponding 2-aryl-2H-benzotriazoles was reported by K. Elbs, et al, J. Prakt. Chem., 108, 204 (1924); Chem. Abst., 19, 514 (1925). The yields of the desired 2-aryl-2H-benzotriazoles varied from 30 to 85% depending on the specific o-nitroazobenzene intermediate reduced.
The known chemical and electrolytic reduction processes for preparing 2-aryl-2H-benzotriazoles are not practical or economically attractive in many cases. The widely used zinc dust and sodium hydroxide system produces effluent pollution problems in respect to waste disposal of zinc sludge which is of increasing environmental concern.
The preparation in good yield of the isomeric, but chemically distinct 1H-benzotriazoles by the catalytic reduction in alkaline medium of o-nitrophenylhydrazine and selected phenyl ring substituted alkyl and perfluoroalkyl derivatives thereof was reported in Japanese patent publication, Sho 48-26012, Aug. 3, 1973. The isomeric 2H-benzotriazoles of this invention cannot be prepared from phenylhydrazines.
It is therefore an object of this invention to provide a novel process for the preparation of 2-aryl-2H-benzotriazoles avoiding severe pollution and environmental problems.
A further object of this invention is to prepare 2-aryl-2H-benzotriazoles by reducing and cyclizing the corresponding o-nitroazobenzene under certain conditions hereinafter set forth in greater detail whereby high yields of the products can be obtained in acceptable purity.